Stainless silver alloy



Patented Nov. 15, 1932 UNITED STATES PATENT. ol -"rIcE 'rAnAsm runs, or ".IOBIG'AIQ FUKUOKA, JAPAN s'rAmLnss SILVER ALLoY in Drawing. Application filed February 12, 1932, Ser1al m. 592,681, and in am scum-{17, "1931.

k The present invention relates to stainless v silver alloy whichcontains 0.5 to 20.0%;of zinc, 10.0 to 40.0% of tin and 50.0 to 89.5% of silver, and the object thereof is to obtain 5 such silver alloy as is hardly stained by air or moisture, especially by sulphides and is easyto cast and work.

In order to manufacture the silver alloy aceording'to this invention, firstly red-heat a crucible in a suitable furnace and charge it with pure silver for melting, preventing the oxidation of the metal such as borax to cover the said metal. After adding the desired quantity of tin and zinc thereto and melting them, together, stir the mixture and then leave it alone for several minutes. When it has settled, pour it into a mold.

Now, with regard to a binary alloy con sisting of tin or zinc added separately to silver, the quantity of the material to be added must be pretty large to maintain the alloy in 'a stainless condition. However, an alloy which contains a large quantity of such material does not only lose the peculiar silvery lustre, but is too hard and brittle to be worked, whereas the alloy according to this invention which is manufactured by adding tin and zinc at the same time is quite free from such defect. It does not only have the lustre peculiar to silver alloy, but is 9.1 most stainless. Moreover, it is tough enough for working. v

In the alloy manufactured by adding tin by adding flux and zinc simultaneously'to silver, if the quanthat according to the present invention the hardness of the alloy increases with the quan-' tity of zinc. By the way, in this experiment the percentage of the weight of tin content is kept at 30% and the quantity of zinc content is increased graduall Ingredients and 1- cent of their weight Test places Hardness 55 Zinc .Tin Silver 100.0 as 0.5 30.0 09.6 43c 5.0 80.0 65.0 69 10.0 30.0 60.0 62 15.0 30.0 55.0 50

-Remarks.The figures described in the "Hardness" col- 4 umn of the above table show Brinells hardness numbers vobtained in applying the load of 5 kilograms to the ball of 1 millimeter diame 1' for one minute.

A (electrolytic silver) Turned black entire- 6 ly in ten minutes B Hardly colored (L- do D do E l; a. d0 85 v(B) When the test pieces were arranged on a glass dish and exposedin the open air for 6 months and their stainness was compared,

A (electrolytic silver) --Turned black entirely in six months (C) The following color standards were made previously by polishing pure silver (purity 99.98%) uniformly with emery paper and immersing the same in decinormal solution of sodium sulphide for difierent time 2- Stendard Duration oi imcolor mersion Cflmng No. 1 2seconds Light yellow.

. 5 seconds Brownish light yellow.

seconds Brownish red increased. seconds- Do. 1 seconds Partially blue.

seconds Blulsh green increased.

seconds Brownish blue increased. seconds. Do.

. seconds. Deep blue, but brown partially.

2 minutes. Brown disappeared. 5 minutes. Almost grey. 10 minutes. Bluish dark grey. 20minutes Do.

When the test alloys according to this invention which consist of the following ingredients were polished uniformly with emery paper and their colors were compared with the above color standards after immersing them in decinormal sodium sulphide solution for tenminutes.

Test places Tin Zinc Silver Per cent 15. 07 Remainder. 8. 1 Remainder. 4. 64 Remainder. 11. 72 Remainder.

Test pieces Coloring F Below No. 1 of the color standards of pure silver. Nearly the same color as when pure silver is immersed in the above reagent for a second. G Same as No. 2. H Same as No. l. K Same as No. 1.

common salt water, and then after left alone for 26 hours, they were taken out at the same time. After cleaning their surfaces with tooth brush, they were dried and weighed. When the change of their weight (gram) was divided by the surface area (square centimeter) of the test pieces, the following figures were obtained':-

Gr. sq. cm.

Copper Decrease 0. 00070 Zinc Decrease 0. 00043 Tin Decrease 0. 000 t1 Silver Increase '0. 00214 Alloy according to this invention Decrease 0. 00016 silver is due to the Remark.'lhe increase of weight in the surface of the dim of silver chloride produced upon test material.

(b) Corrosion test with acetic acid. After boiling the above five kinds of test pieces in 10% acetic acid solution for ten minutes by the same process with the above, they were left alone for 8 hours and the decrease of their weight was examined.

Gr. sq. cm. Copper Decrease 0. 00038 Zinc Decrease 0. 03889 T in Decrease 0. 00070 Silver- -i Decrease 0. 00050 Alloy according to this invention De crease 0. 00010 Fromthe above tables it will be seen that made according to this invention show the least decrease.

As already stated, the alloy of this inven tion is not only hardly colored but almost non-corrosive. As compared with the annealed pure silver which has the tensile strength of 14 kilograms per square mlllime ter, the elongation of 40 o (Brinell) of 23, it has of about 20 kilograms per square millimeter, the elongation of about 11% and the hardness (Brinell) of about 60. Thus, although it shows more or less decrease in the elongation and the hardness the tensile strength as compared with pure silver, an increase 1s seen in the tensile strength and hardness.-

it is so hard as to be suitable Consequently, for the materialfor table-wares and other kinds of wares. Although there is more or less the decrease in its elongation, and the increase in the tensile strength and hardness, it is not so brittle as to be difiicult to work. Now, pure silver ina fused state absorbs oxygen of the volume nearly twenty-three times as large and liberates it on solidification and is apt to produce gas holes in a'cast article, whereas the alloy according to this invention containing zinc and tin which act as deoxidizers, they drive away the oxygen which would be absorbed in fused silver, thus making it possible to produce easily a cast article cases, etc.

I clalm.

A stainless alloy consisti of 0.5-20.0% of zinc, 10.0-40.0% of tin an (SOD-89.5% of silver.

TADASHI TANABE. 

